The possibility of achieving line widths of one micron or less on semiconductor surfaces with photolithographic projection printers operating in the near ultraviolet (.about.0.4 microns) seems remote. The state of the art in refracting systems is represented by commercially available step and repeat cameras which are capable of printing 1.5-2 micron lines anywhere within a 14 millimeter diameter field.
Recently, photoresists sensitive to the far ultraviolet (.about.0.215 microns) have been developed. For a given aperture, halving the wavelength doubles the resolution. Thus, operation with the new photoresists in the far ultraviolet should yield a two-fold reduction in line widths.
Accordingly, efforts have been directed at trying to design a diffraction-limited photolithographic projection apparatus capable of operating in the far ultraviolet (.about.0.215.mu.). It was recognized that such apparatus, if available, would be a significant contribution to the field of submicron photolithography.